Process for the preparation of aminotriazine derivatives

A process for the preparation of 4-amino-3-oxo-2,3,4,5-tetrahydro-1,2,4-triazine derivatives of the formula I ##STR13## wherein R.sub.1 is hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.3 -C.sub.6 cycloalkyl, C.sub.1 -C.sub.4 alkoxy-C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.2 haloalkyl, phenyl, benzyl, phenethyl, phenpropyl, phenbutyl or phenpentyl, or a phenyl, benzyl, phenethyl, phenpropyl, phenbutyl or phenpentyl radical that is mono- or di-substituted by halogen, C.sub.1 -C.sub.5 alkyl, C.sub.1 -C.sub.2 haloalkyl, methoxy and/or ethoxy;

• R.sub.2 is hydrogen, C.sub.1 -C.sub.6 alkyl or C.sub.3 -C.sub.6 cycloalkyl, or is phenyl that is unsubstituted or substituted by C.sub.1 -C.sub.12 alkyl, halogen or by C.sub.1 -C.sub.12 haloalkyl, or R.sub.1 and R.sub.2 together form a saturated or unsaturated 3- to 7-membered carbocycle, and R.sub.3 is hydrogen or C.sub.1 -C.sub.6 alkyl, by the solvolysis of compounds of the formula II ##STR14## wherein R.sub.4 is H, C.sub.1 -C.sub.4 -alkyl, C.sub.3 -C.sub.6 -cycloalkyl, C.sub.1 -C.sub.4 -alkyl substituted by 1 to 9 chlorine atoms, C.sub.1 -C.sub.3 -alkoxy, C.sub.1 -C.sub.3 -alkylthio, phenyl, pyridyl, or phenyl or pyridyl which is substituted with 1 to 3 substituents selected from the group of halogen, methyl, ethyl, methoxy, methylthio or nitro,
• in the presence of gaseous hydrogen chloride in an alcoholic medium.